Nichiren Daishonin states in “On the Transmission of the Three Great Secret Laws”:
There are two types of Daimoku: the Daimoku chanted during the Former and Middle Days of the Law, and the Daimoku to be chanted during the Latter Day of the Law. Although Bodhisattvas Vasubandhu and Nagarjuna themselves chanted the Daimoku during the Former Day of the Law, they did so to practise for themselves only. During the Middle Day of the Law, Nanyue, Tiantai, and others did chant the Daimoku; however, they did it only for the sake of their own practice and not for teaching others. This type of Daimoku was practiced based on the theory. Now, in the Latter Day of the Law, the Daimoku that Nichiren chants is different from that of previous ages. It is the Nam-Myoho-Renge-Kyo of the practice for oneself, and the practice for others.